1. Field of the Invention
The present invention relates to a surface mounting type light emitting diode. In particular, the present invention relates to a surface mounting type light emitting diode attaching importance to heat radiation performance, reliability and productivity, and to a method for manufacturing the same.
2. Description of the Background Art
A semiconductor light emitting element emits visible light or near infrared light in such a manner that a PN junction is formed on an AlInGaP compound semiconductor wafer or a GaN compound semiconductor wafer and forward electric current is fed to the PN junction. In recent years, the semiconductor light emitting element has been widely adopted for use in display, communication, measurement, control and the like. Further, the semiconductor light emitting element tends to be used in a field of automotive components requiring good heat radiation performance and high reliability. There has been also developed a surface mounting type light emitting diode for satisfying such requirements.
As shown in FIG. 16, a conventional surface mounting type light emitting diode 100 has the following structure. That is, a semiconductor light emitting element 103 is mounted on a substrate 101 having electrodes 102. Semiconductor light emitting element 103 has electrodes connected to electrodes 102 of substrate 101 through electric conductive wires 104 by a wire bonding process. Substrate 101 includes a molding member 105.
When a semiconductor light emitting element (an LED chip) mounted on a surface mounting type light emitting diode emits light, heat is generated from the LED chip. As electric current to be fed to the LED chip is large in amount, the heat generated from the LED chip becomes large in amount. In such an LED chip, typically, as a temperature increases, light emission efficiency deteriorates and degradation of emitted light becomes noticeable. In other words, even when a large amount of electric current is fed to the LED chip, intensity of light emitted from the LED chip is not improved effectively, and a lifetime of the LED chip shortens disadvantageously. In order to avoid such disadvantages, the heat generated from the LED chip is effectively radiated to the outside so as to decrease the temperature of the LED chip. Thus, the LED chip can ensure good light emission efficiency and good lifetime characteristic even when a large amount of electric current is fed thereto.
Examples of the foregoing conventional semiconductor light emitting device with improved heat radiation effect are disclosed in Japanese Patent Laying-Open Nos. 11-046018, 2002-222998, 2000-058924, 2000-077725, 2000-216443 and the like. In Japanese Patent Laying-Open Nos. 11-046018 and 2002-222998, the heat radiation performance can be improved in such a manner that a surface area of a lead frame is enlarged. In Japanese Patent Laying-Open Nos. 2000-058924, 2000-077725 and 2000-216443, on the other hand, the heat radiation performance can be improved in such a manner that a substrate is made of metal superior in heat conductivity to resin.
In conventional surface mounting type light emitting diode 100 shown in FIG. 16, however, the heat generated from semiconductor light emitting element 103 is received only by electrodes 102. Consequently, the heat radiation performance of conventional surface mounting type light emitting diode 100 is unsatisfactory. In addition, the reliability of conventional surface mounting type light emitting diode 100 is also unsatisfactory in a case where conventional surface mounting type light emitting diode 100 is used as an automotive component in severe environment-resistant conditions (e.g., temperature, vibration). In order to arrange a fluorescent material (a fluorescent substance) in a reflector for reflecting light emitted from semiconductor light emitting element 103, molding member 105 for covering semiconductor light emitting element 103 must contain such a fluorescent material. However, a resin containing the fluorescent material is degraded by exposure to high-temperature heat generated from semiconductor light emitting element 103, in the vicinity of semiconductor light emitting element 103. Consequently, the lifetime of conventional surface mounting type light emitting diode 100 serving as a light source shortens disadvantageously.